iPod touch sync issue

Hey ya'll I'm not sure what gen iPod touch I have but it's an 8gig and iOS 4.2.1 is the newest version of the os it can run...

I have never had an issue with it before. But I was d/l some new music on my macbook and synced it. It popped up and said, "The song "Fade Away" was not copied to the iPod because the song cannot be played on this iPod."

I just bought 4 albums and updated my playlists (all form my macbook) and have been getting this error. Everything else synced just fine including every other song on this same album ... Coincidentally it synced just fine to my iPhone4s .... Any thoughts / suggestions?

Thanks

My first apple product is this White 2.4 Mac Book I bought on September 25, 2008!

Also, just to clarify, do you only get this error on newly purchased music? When did you buy the music? Is older purchased music working properly? What file format of purchased music is working? What file format isn't?* Are you running the latest version of iTunes? Is your computer authorized?

*There is a difference between .m4a and .m4p, .m4a is older with DRM restrictions and .m4p is newer iTunes Plus without restrictions.